Field of the Invention
The present disclosure relates to imaging sensors, and more specifically, to an imaging sensor coupled with layered filters.
Background
FIG. 1A shows a typical digital imaging device 100 including a lens 120 (or lens system) and an image sensor 130. In FIG. 1A, an object 110 reflects light 112 that is focused by the lens 120 onto an image sensor 130 as an image object 114. The image sensor 130 includes photosensitive elements or sensels 132 which are distributed over the surface of the image sensor 130 in a two-dimensional array. The sensels 132 generally convert the light focused onto the surface of the image sensor 130 by the lens 120 (i.e. the image object 114) into electronic signals.
A digital camera includes a sensor to capture the color signal of objects using a color filter array (CFA), which has one color filter element for each sensel. Thus, the color filter element manages one color sample at a time. The CFA is used to capture all three color channels at the same time and reduce the complexity and cost of the digital cameras. Thus, in a conventional color imaging device, each of the sensels 132 receives light within one of three overlapping frequency bands. The relative intensity of the light received by an individual sensel 132 included in a group of sensels 140 (in which each of the different frequency bands are represented) enables the image sensor 130 to provide color information.
FIG. 1B illustrates a Bayer pattern which is widely-used CFA pattern. The sampling of green (G) color component 142 is twice as many as compared to each of red (R) 144 and blue (B) 146 color components. As shown in FIG. 1B, at each pixel (configured with a sensel), only one color component is present. The missing two colors have to be interpolated from the existing pixels. The process of reconstructing a full resolution color image from Bayer sample is known as demosaicing. An inherent limitation in the interpolation process leads to visual artifacts that appear around edges and color mis-registration artifacts that degrade the color resolution. Thus, the reconstruction of the color image from the data attained by the monochromatic sensor filtered by the CFA (e.g., in a demosaicing process) results in a loss of spatial resolution.